how to add redirect page in shopify plus?

How to add a simple page which says "Wait while we redirect you" and then redirect to custom payment/loyalty page in shopify. We have shopify+ account & our own loyalty point (manual payment method setup).

So for example below:

1. customer on checkout page:

2. now customer on redirect page like below:

3. the customer on the custom payment page.

Now, I wanted to create redirect page and if my customer select certain payment/loyalty option then they will redirect to the point 2) screenshot and then go to point 3) but if they decided to go from point 3) to point 1) then the order should not be created in shopify.

so we are skipping processing step where order has been created.

I've done lots of research on this by looking different options. Please do not suggest additional script as we got the shopify plus store where I want to create redirect page and skipping order creation at that point. I know window.location but this is not I am looking for.

My reserach: checkout liquid shopify

Editing checkout page best practices

I know we can achieve this by using below but not sure how:

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